JPS6315422A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an silicon thin-film section having thickness having high precision with excellent reproducibility by using an SOI substrate as a starting material and conducting selective etching through anisotropic etching, employing a nitride film or an oxide film as an etching preventive layer from the substarte side. CONSTITUTION:Pressure-sensitive resistance layers 6 and a wiring pattern are formed to the surface, and a first silicon oxide film 5b and a second silicon nitride film 8b on the back side of an SOI substrate are patterned through photolitho-etching. A first silicon nitride film 2 is exposed through anisotropic etching by a potassium hydroxide liquid, using the patterns of the first silicon oxide film and the second silicon nitride film as masks, and a thin section 10 as a diaphragm is shaped, thus completing a semiconductor pressure sensor. The first silicon nitride film functions as an excellent etching stopping layer at that time, thus easily controlling thickness with superior reproducibility and high accuracy without precisely controlling the etching time.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and in particular, to a method for manufacturing a semiconductor device including a silicon thin film portion and a support portion extending to the thin film portion. Regarding the method.

[Prior art and its problems]

With advances in semiconductor technology, semiconductor pressure saw sensors that utilize the rainbow resistance effect of semiconductors such as silicon and germanium have been attracting attention in recent years.

Various structures have been proposed for half-solid pressure sensors, but the most widely used one is one made of single-crystal silicon with a diffusion layer 101a as a pressure-sensitive resistance layer, as shown in FIG. This is a diaphragm-type pressure sensor in which a diaphragm 101 is adhesively fixed to a pedestal 102. 10
3 is an adhesive layer.

This pressure sensor detects a change in resistance value that occurs when a diaphragm is subjected to pressure and is distorted. Therefore, it is necessary to form a diaphragm that generates the correct strain depending on the pressure. For this reason, the thickness t of the diaphragm needs to be uniform and needs to be as designed.

When manufacturing, normally, after forming a diffusion layer 101a as a pressure-sensitive resistance layer or an electrode (not shown) in a silicon substrate, the surface of the silicon substrate is covered and protected with a resist, and a resist R is applied to the surface. pattern is formed by photolithography.

(FIG. 4(a)) Then, using potassium hydroxide (KOH) as an etching liquid, the silicon substrate is etched from the back side to form a thin portion as a diaphragm.

(FIG. 4(b)) Since the thickness of the diaphragm greatly affects the performance of the pressure sensor, various efforts have been made to improve the etching accuracy.

For example, there is a method of controlling the etching amount (depth) by adjusting the etching time based on the etching rate of the etching solution used.

In this method, due to unevenness in the thickness of the silicon substrate as a starting material, deterioration of the etching solution, etc., it was necessary to use a solid piece to accurately form the thickness of the thin part of the die (7 flams).

Further, as shown in FIG. 5(a), an n-type silicon substrate 20
．． After forming a P medium silicon layer 201 on the surface of (
The starting material is a silicon thin film layer 202 (of i-type) formed by epitaxial growth, and the P
There is a method of using a green silicon layer as an etch stop layer. In this method, first, a diffusion layer 202a, electrodes (not shown), etc. are formed within this silicon thin film layer 202. Then, in the same manner as described above, after covering the front surface with resist R and the pattern of resist R, the P medium silicon layer 201 as an etching stop layer is exposed from the back side as shown in FIG. 5(b). A method is used in which etching is continued until desired.

However, even with this method, the etching selectivity between the P+ silicon layer and the n-type silicon substrate is at most 10 to 20.
Because of this, the etching time tolerance is small. Additionally, when forming the P-type silicon layer, auto-doping causes impurities to diffuse onto the silicon substrate surface, causing the interface between the P-type silicon layer and the n-type silicon substrate to move, which also affects the thickness of the die suffragm due to etching. This causes unevenness.

Furthermore, although a method of electrically measuring and controlling the etching rate has been proposed, the device is complicated, so it is not suitable for mass production, and it is impossible to form patterns with complicated shapes.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to form a thin silicon portion with high dimensional accuracy.

[Means for solving problems]

Therefore, in the present invention, a nitride film or oxide film is formed on the surface of a silicon substrate, and then a silicon thin film layer of a desired thickness is formed as a starting material, and the nitride film or oxide film is anisotropically etched as an etching stop layer. The silicon substrate is selectively removed from the back side by etching to form a thin silicon portion having a desired shape.

(Function) For example, silicon nitride film (Si3N4), boron nitride film (
8N) etc. have a selectivity of at least 300 times higher than anisotropic edgeants for silicon such as potassium hydroxide, so there is a large margin of etching time and it is extremely easy to etch by simply immersing it in the etchant. Formable. Furthermore, it is possible to reduce the thickness of the etching stop layer.

Furthermore, since the interfaces between the silicon substrate, nitride film, and silicon thin film are sharp, the silicon 77 film can be formed with precise film thickness.
! A thin portion made of Iv and a nitride film is formed.

C Embodiment] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) to 1(0) explain the manufacturing process of a semiconductor pressure sensor according to an embodiment of the present invention.

First, as shown in FIG. 1(a), a first silicon nitride film 2 as an insulating layer with a film thickness of 0.5 m is deposited on an n-type silicon substrate 1 with a thickness of 300 IIIn and oriented in the (100) direction. SOI (5 silicon oninsula) is formed by depositing a silicon thin film layer 3 with a thickness of 10 -
(tor) Prepare a substrate hill. The silicon thin WA layer 3 is formed by being intermediately crystallized by annealing after deposition, and uses a portion of the underlying (100) silicon substrate 1 as a seed, so that it has the same surface orientation.

Next, as shown in FIG. 1(b), by the hot acid method,
First silicon oxide films 5a and 5b having a thickness of 0.5 cap are formed on both sides of the SOI substrate.

Thereafter, as shown in FIG. 1(C), a diffusion window W is formed on the surface of the SOI substrate hill by photolithography, and poron (B) is diffused through the window W. After a step (heat treatment in an oxidizing atmosphere), a P-type diffusion layer 6 as a pressure-sensitive resistance layer is formed. At this time, a second acid 1-arsenic silicon film 7 is formed on the surface.

Subsequently, as shown in FIG. 1(d), the SO
A second silicon nitride film 3a is formed on the front and back surfaces of the I-substrate 4.
, 3b are deposited, and contact holes H are formed in the silicon nitride IIQ 8a on the surface side by photolithography.

Furthermore, an aluminum thin film is formed by electron beam evaporation and patterned by photolithography to form a wiring pattern 9.

(FIG. 1(e)) After forming the pressure sensitive resistance layer 6 and the wiring pattern 9 on the surface in this way, the S
The first silicon oxide IIQ5b and the second silicon nitride IIQ8b on the back side of the OI substrate are buttered.

(FIG. 1(f)) Finally, using the patterns of the first silicon oxide film and the second silicon nitride film as masks, anisotropic etching is performed using a potassium hydroxide solution to remove the first silicon nitride film. Dew membrane 2? Finally, as shown in FIG. 1(g), a thin portion 10 as a diaphragm having a thickness of 10 times is formed, and a semiconductor pressure sensor is completed.

Here, since the etching selectivity of the (first) silicon nitride film to potassium hydroxide is 300 times or more that of the n-type silicon substrate 1, the first silicon nitride film serves as a good etching stop layer. Therefore, without strictly controlling the etching time, it is possible to easily obtain a semiconductor pressure sensor having a diaphragm with good reproducibility and whose thickness is controlled with high precision (±11 En).

In addition, the (first) silicon nitride film used as the etching stop layer has an extremely sharp interface with the n-type silicon substrate 1 and the silicon thin film layer 3, and has high etching selectivity, so it is sufficient even if it is thin. Therefore, it is possible to improve the sensor characteristics. Furthermore, the thickness of the thin portion is also uniform. Furthermore, the SOI substrate can be used as it is as a starting material, making manufacturing extremely easy.

In the embodiment, a silicon nitride film is used as the insulating layer of the SOI substrate, but a nitride film such as a boron nitride film or an oxide film such as silicon oxide ffQ may also be used. By the way,
The etching time for a silicon oxide film is 1/20 that of the etchant used for anisotropic etching of silicon.
It is 0 times or less.

Further, the etchant is not limited to potassium hydroxide, and it goes without saying that other etchants may be used.

In addition, in the embodiment, a semiconductor pressure sensor was described, but the present invention is not limited to this, and as shown in FIG.
As shown in (b), it is applicable not only to the formation of cantilevers and beams, but also to semiconductor devices that can be etched from the surface, leaving only oxide films and nitride films in the form of beams or bridges. It goes without saying that there is.

(Effects) As described above, according to the present invention, when forming a silicon thin film portion, an SOI substrate is used, in which a silicon thin film is formed on a silicon substrate via a nitride film or an oxide film as an insulating layer. Since the H material is selectively etched from the substrate side by anisotropic etching using the nitride film or oxide film as an etching stop layer,
It becomes possible to form a silicon thin film portion with good reproducibility and a highly accurate thickness.

[Brief explanation of drawings]

FIGS. 1(a) to (g) are manufacturing process diagrams of a semiconductor pressure sensor according to an embodiment of the present invention, and FIGS. 2(a) and (b) are diagrams showing other application examples of the method of the present disclosure. Figure 3 is a diagram showing an example of the structure of a normal semiconductor pressure sensor, Figures 4 (a) and (b)
and FIGS. 5(a) and 5(b) are diagrams showing the conventional process of forming a diaphragm (thin wall portion), respectively. DESCRIPTION OF SYMBOLS 101... Diaphragm, 101a... Diffusion (resistance) layer, R... Resist, 200... N-type silicon substrate, 201... P-type silicon layer, 202... Silicon thin film layer, 202a ... Diffusion layer, 1... N-type silicon substrate, 2... First silicon nitride film, 3... Silicon thin film layer, 4... SOI substrate, 5a, 5b...
First silicon oxide film, 6... P-type diffusion layer (pressure sensitive resistance layer), 7... Second silicon oxide film, 8a, 8b...
・Second silicon nitride film, 9...wiring pattern, 1o
...thin part. Figure 1 (Q) Figure 1 (e) Figure 1 ((1) Figure 2 (Q) Figure 4 (0) Figure 4 (b) Figure 5 (b)

Claims (5)

[Claims] (1) In a method for manufacturing a semiconductor device having a silicon thin film portion, an SOI (Silicon On Insulator) is formed by forming a nitride film or an oxide film as an insulating layer on the surface of a silicon substrate as a starting material and further forming a silicon thin film.
r) an etching step of forming the silicon thin film portion by selectively etching a predetermined region of the SOI substrate from the silicon substrate side by anisotropic etching using the substrate and using the insulating layer as an etching stop layer; A method for manufacturing a semiconductor device, comprising: (2) The nitride film is silicon nitride (Si_3N_4)
A method for manufacturing a semiconductor device according to claim (1), characterized in that the method comprises: (3) The method for manufacturing a semiconductor device according to claim (1), wherein the nitride film is made of boron nitride (BN). (4) The method for manufacturing a semiconductor device according to claim (1), wherein the oxide film is made of silicon oxide (SiO_2). (5) The anisotropic etching step includes potassium hydroxide (
The method for manufacturing a semiconductor device according to any one of claims (1) to (4), characterized in that the step uses KOH as an etchant.